The present invention relates to a blow-bye gas return device for internal combustion engines, whereby the blow-bye gas can be returned to the upstream side of a throttle valve.
As is disclosed, for example, in Japanese Utility Model Laid-Open Publication (Kokai) No. 59-7211 published Jan. 18, 1984, well known to those skilled in the art is a blow-bye gas return system of the type in which the blow-bye gas within the cylinder block is returned through a blow-bye gas passage and a PCV valve to the downstream side of the throttle valve while a discharge orifice of another blow-bye gas passage is opened at the upstream side of the throttle valve so that when the internal combustion engine is required to operate at high speed under high load, the blow-bye gas is induced through the discharge orifice.
Meanwhile, in order to simplify the construction of the fuel supply system for internal combustion engines, there has been devised and proposed a system in which a fuel injector body and a throttle body are provided as a unitary construction in such a way that a fuel injector is disposed at a position immediately upstream in relation to the throttle valve and in which a hot-wire type air flow sensor is disposed at one side of the air passage through the injection body.
However, there arises the problem that because the air flow sensor is of the hot-wire type, measures must be taken for reducing the polution of the flow sensor film to a minimum so that the flow sensor output can be maintained at a high degree of accuracy. As is well known in the art, in the air flow sensor of the type described above, a hot-wire made of a platinum wire is disposed in the air flow passage and the quantity of heat derived by the air flowing past the hot wire is electrically sensed to measure the quantity of intake air. Therefore, when dust particles, oil mist, gasoline vapor and the like, adhere to the surface of the hot wire, measurement errors occur and consequently the fuel injection timing control as well as the ignition timing control cannot be carried out correctly. In particular, oil mist operates as an adhesive agent, causing the dust particles to adhere to the hot wire so that the flow of oil mist to the upstream side of the air flow sensor must be avoided. It therefore follows that on the upstream side of the throttle valve, the discharge orifice through which the blow-bye gas is returned, should not be opened at a position upstream of the air flow sensor.
However, in the case of the unitary construction of the throttle body and the injection body, the distance between the throttle valve and the fuel injector is extremely short so that when the discharge orifice is opened at a position downstream of the fuel injector, there arises the problem that gasoline or fuel is sucked to the blow-bye gas passage through the discharge orifice, causing so-called oil dilution.